Although 鰤 is one character, it can be decomposed into two characters, 魚 and 師.As you may know, each kanji has its meaning.魚 means a fish. Buri is absolutely a fish.That’s why the kanji of Buri has 魚.

How about師? 師 has some meanings.
One of the meanings is a honorific title for a Buddhist monk.
It is said that Buddhist monks are generally busy in the end of year.
Buddhist monks run here, there and everywhere in December.
The truth is not clear.
It is said that the number of death grows towards the end of the year.
It is said that Buddhist monks do a year-end cleaning at their temples.